It is now commonly accepted that the vision impairing disease known as cataracts can be alleviate by surgically replacing the natural lens of the eye with an artifical intraocular lens. The condition of cataracts is characterized by the clouding of the natural lens of the eye so that the amount of light which reaches the retina is substantially reduced or completely eliminated.
The anatomy of the eye 1 is shown schematically in FIG. 5. The cornea 2 forms the front surface of eye 1 and connects with the ciliary muscle 3, from which the iris 4 extends. Iris 4 divides the front portion of eye 1 into the anterior chamber 5, between iris 4 and cornea 2, and a posterior chamber 6 behind iris 4. The capsular bag 7 in which the natural lens of the eye is encased is supported from ciliary muscle 3 by suspensory ligaments 8, called zonules. Pupil 9 is the aperture at the center of iris 4 through which light passes to posterior chamber 6 and to the back of the eye (not shown).
It is possible to remove a cataract len by cryogenic, mechanical or ultrasonic procedures.
The cryogenic techniques uses an insulated probe to freeze the lens into a solid mass to permit the frozen mass to be gripped and removed as a complete structure from capsular bag 7.
Mechanical means for removing the lens are shown for example in U.S. Pat. No. 4,002,169 where a small surgical tool is introduced into the eye by inserting a specially constructed hollow needle into the eye behind a rotary augering tool journaled in the hollow needle. Surgical procedures may then be performed with the rotary tool or with different tools inserted through the needle cannula to remove unwanted tissue such as cataracts. A rotary masticating tool may be introduced through the hollow needle. The unwanted tissue can then be masticated or liquified and then withdrawn through the needle bore following removal of the masticating tool. Similarly fluids may be injected into the body and withdrawn from the body through the hollow needle.
Ultrasonic removal of the cataract can be accomplished by the instrument and procedure shown, for example, in U.S. Pat. No. 3,589,363. That apparatus includes a casing in which is mounted a vibratory assembly for converting electrical energy into a high frequency mechanical vibrations which are used to break apart the unwanted cataract.
A transducer is located inside the casing and is connected to a acoustic impedence transformer or horn which has a relatively massive input section, a slender output section and a tapered transition section. The geometry of the horn can be designed to achieve the desired sonic wave form. A tip, usually a hollow cannula, can be attached to the distal end of the horn.
There are passages through the instrument for introducing (irrigating) treatment fluid to the region where the vibrations are applied to the eye and other passage for carrying away (aspirating) a slurry of unwanted material and treatment fluid from the eye.
The fluid lines cannot be directly attached to the vibrator assembly since that could dampen the vibration and cause loss of efficiency. In order to aspirate fluid through the ultrasonic instrument, aspiration holes are drilled through the casing and the horn. A chamber is created between the casing and the horn by placing flexible "O" rings around the horn and against the casing on either side of the aspiration holes. The aspiration line enters the chamber to provide negative pressure which is transmitted through the horn and the attached cannula to the operative site. Additional "O" rings may be used to establish separate irrigation passages.
Although present ultrasonic aspirators work satisfactorily, the use of "O" rings creates a maintenance problem. It would be desirable to have a ultrasonic device for emulsifying unwanted tissue, which would eliminate the need for "O" rings but would still maintain fluid passages without leakage for irrigation and/or separate aspiration.